[llvm-commits] [llvm] r52397 - /llvm/trunk/lib/Transforms/IPO/IPConstantPropagation.cpp

[Matthijs Kooijman]

Author: matthijs
Date: Tue Jun 17 07:20:24 2008
New Revision: 52397

URL: http://llvm.org/viewvc/llvm-project?rev=52397&view=rev
Log:
Learn IPConstProp to propagate arguments that are directly returned. Strictly
speaking these are not constant values. However, when a function always returns
one of its arguments, then from the point of view of each caller the return
value is constant (or at least a known value) and can be replaced.


Modified:
    llvm/trunk/lib/Transforms/IPO/IPConstantPropagation.cpp

Modified: llvm/trunk/lib/Transforms/IPO/IPConstantPropagation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/IPConstantPropagation.cpp?rev=52397&r1=52396&r2=52397&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/IPO/IPConstantPropagation.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/IPConstantPropagation.cpp Tue Jun 17 07:20:24 2008
@@ -145,6 +145,10 @@
 // all callers that use those return values with the constant value. This will
 // leave in the actual return values and instructions, but deadargelim will
 // clean that up.
+//
+// Additionally if a function always returns one of its arguments directly,
+// callers will be updated to use the value they pass in directly instead of
+// using the return value.
 bool IPCP::PropagateConstantReturn(Function &F) {
   if (F.getReturnType() == Type::VoidTy)
     return false; // No return value.
@@ -188,8 +192,8 @@
           if (isa<UndefValue>(V))
             continue;
           
-          // Try to see if all the rets return the same constant.
-          if (isa<Constant>(V)) {
+          // Try to see if all the rets return the same constant or argument.
+          if (isa<Constant>(V) || isa<Argument>(V)) {
             if (isa<UndefValue>(RV)) {
               // No value found yet? Try the current one.
               RetVals[i] = V;
@@ -255,6 +259,11 @@
       if (index != -1) {
         Value *New = RetVals[index];
         if (New) {
+          if (Argument *A = dyn_cast<Argument>(New))
+            // Was an argument returned? Then find the corresponding argument in
+            // the call instruction and use that. Add 1 to the argument number
+            // to skipp the first argument (the function itself).
+            New = Call->getOperand(A->getArgNo() + 1);
           Ins->replaceAllUsesWith(New);
           Ins->eraseFromParent();
         }